Field of the Invention
The invention relates to a turbine, in particular a steam turbine, which is oriented along a rotational axis and includes a turbine blade. The turbine blade is oriented along a blade axis and has a head region and a blade region adjoining the head region. The steam turbine also includes a turbine component extended along the rotational axis, a mainstream course with a mainstream direction, and a gap flow course communicating fluidically with the mainstream course and leading through a sealing gap between the head region and the turbine component. The blade region makes it possible to deflect an action fluid, which can be carried through the mainstream course, by a circumferential angle. The invention also relates to a turbine blade that is oriented along a blade axis and has both a head region and a blade region adjoining the head region. The blade region deflects an action fluid by a circumferential angle.
An impulse or action steam turbine with a rotor, a stator and a plurality of stages is described in European Patent 0 509 921 B1. Each stage has one fixed set of blades and one movable set of blades. The fixed set of blades accomplishes more than 85% of a pressure drop at the base of each stage. The movable set of blades is mounted directly on the rotor. The fixed set of blades has a shroud on an inner ring, with a base diameter that is substantially equivalent to the diameter of the rotor. A seal is also provided, for sealing off the stationary set of blades from the rotor. European Patent 0 509 921 B1 discloses a plurality of different embodiments both for the seal and for a flow course of fluid emerging from the seal. In one embodiment, both the shroud on a downstream side and a guide blade following the shroud, in a root region, are chamfered so that fluid flowing through the seal flows essentially axially into a mainstream of the fluid.
A wall contour for an axial turbomachine is described in later-published European Patent Application 0 799 973 A1. In particular, the wall contour pertains to a channel contour in the bladed region of a steam turbine and can be used for sets of blades that have tip seals or those which have shroud plates or shroud plate seals. European Patent Application 0 799 973 A1 describes provisions that are intended to improve a reentering flow of a labyrinthine mass flow between a rotor blade and the wall contour. The shroud band of the rotor blade or the shroud band of the guide blade is lengthened in the axial direction in that case and cut in such a way that a labyrinth exit is radially as narrow as possible, to avoid unnecessary dissipation. Due to the lengthening of the shroud plate, the outflow from the labyrinth can occur as close as possible to the following guide blade inlet.
In Patent Abstracts of Japan, Vol. 007, No. 221 (M-246), Sept. 30, 1983, for Japanese Patent Application published under No. 58 113504, a plurality of slots are disposed in a housing of an axial turbomachine. Those slots have a rectangular cross section. The slots are shaped in such a way that at each end point of a rotor blade adjacent the housing, the direction at every point of the slot agrees with the direction of the absolute velocity vector of the fluid at the end of each point of the rotor blade.
Swiss Patent 529 914 discloses a turbine stage of a turbine which is used, for instance, for driving an electrical generator or an aircraft engine. An intermediate space is formed between a false bottom of a guide blade and a rotor disk, through which a leakage flow of operating medium can flow. In a transitional region from the intermediate space to the rotor blade, a protrusion is provided, which is constructed in the form of a ring and partly covers the root surface of the rotor blade. As a result, an annular gap is formed with the root surface for the passage therethrough of some of the operating medium, referred to as a leakage flow. Grooves are constructed on an inside surface of the protrusion and extend at an angle that is identical to the exit angle of the guide blade. Providing the oblique grooves on the inside surface of the protrusion lends the leakage flow a spin toward the side of the rotation of the rotor wheel of the turbine stage. The swirling leakage flow leads energy to the utilization of the leakage flow at the rotor blades of the rotor, which is intended to increase the efficiency of the turbine stage.
In an article by J. D. Denton, entitled "Loss Mechanisms in Turbomachines" in ASME Paper 93-GT-439, 1993, the American Society of Mechanical Engineers, various loss mechanisms that reduce the efficiency of a steam turbine are described, and a quantitative and qualitative assessment of those losses is provided. A substantial proportion of the loss, that counts as one of the causes of fluidic loss, is due to what is known as gap loss, which can amount to up to about 30% of the total loss. The gap loss arises upon a flow through a sealing portion between a fixed component and a rotating component of the steam turbine. The fluid flowing through the sealing portion then re-enters the mainstream of the fluid. The sealing portion acts in that case to seal off the rotating component from the fixed component, for instance in order to seal off a rotor blade from the turbine housing and a guide blade from the turbine shaft. The magnitude of the gap loss is proportional, among other things, to the proportion of the mass flow flowing through the seal to the main mass flow, depending on the velocity ratio of the fluid in the gap and in the mainstream and on the angle at which the fluid emerges from the gap into the mainstream. According to Denton, the latter, because of the difference in temperature and velocity between the mainstream and the gap flow, leads to a temperature increase and thus to an additional loss of efficiency.